Technology for observing and collecting information about cells and living body tissue by detecting scattered light from a living body when light is illuminated onto the cells of living body tissue is already known. For example, International Patent Publication WO 00/43750, discloses a system for measuring the size distribution of cell nuclei in a living tissue by detecting the back-scattered light from the living tissue in different directions and for making visible the abnormality of the cells by displaying the scattered light on a display device.
In summary, in the system, a living tissue is irradiated by illumination light and the spectral intensity distribution of the scattered light from the living tissue is detected. This enables one to determine information regarding particles in the living tissue, such as the diameter and the refractive index of the particles. It is known that the nuclei of cancerous cells are larger in size than the nuclei of normal cells. Therefore, by measuring the back-scattering characteristics of the light that is scattered by the living tissue, one can predict whether the cells that scatter the light are cancerous or normal.
The scattered light from living body tissue includes both single scattering components and multiple scattering components. Since information of interest relating to the particles is included primarily in the single scattering components, it is desirable to remove the multiple scattering components. As one method of doing this, the scattered light is detected at multiple angles, and a calculation is made of the scattered light intensity between these angles.
In the prior art example mentioned above, as a specific construction for accomplishing detection at multiple scattering angles, an explanation is provided of an example which uses a single illumination optical system and multiple detection optical systems. If the detection optical system is multiple, then—particularly in the case of observing the scattering spectrum information with an endoscope—, the size of the front part of the endoscope becomes large.